The present invention generally relates to a heat treating process and more particularly, to a continuous heat treating furnace for heat-treating a metallic strip and the like therein.
Conventionally, in the continuous heat treating furnaces for a metallic strip, etc., heat treatment is effected by heating and soaking the metallic strip at a predetermined temperature and cooling said metallic strip thereafter, but heat discharged from the metallic strip during the cooling thereof is undesirably dissipated into the atmosphere at it is, without being utilized, thus resulting in a loss of energy to a large extent.
Accordingly, in order to prevent the loss of energy in the continuous heat treating furnace for a metallic strip as referred to above, there has been proposed, in Japanese Patent Application Tokugansho No. 58-112328 assigned to the same assignee as the present invention, a continuous heat treating furnace for a metallic strip, which comprises a furnace body, a heat exchanging zone (pre-heating/pre-cooling zone) for pre-heating and pre-cooling the metallic strip, and a heating/soaking zone for heating and soaking the metallic strip, said heat exchanging zone and heating/soaking zone being provided within the furnace body by dividing the interior of said furnace body with a partition wall disposed in a direction of width of the furnace body so as to transport the metallic strip in a confronting state through the heat exchanging zone, said heat exchanging zone being provided with nozzle means for jetting atmospheric gas of the heat exchanging zone onto opposite surfaces of said metallic strip being transported, an atmosphere supply duct means for the nozzle means, and a circulation fan for utilizing heat dissipated from the metallic strip during pre-cooling for pre-heating the metallic strip in order to achieve energy saving.
In the continuous heat treating furnace for the metallic strip as described above, however, the control of heat curves is to be effected through an increase or decrease of heat conductivity by the adjustment of air flow of the circulating fan, and such an increase or decrease is limited in itself, thus making it impossible to fully cope with the situation in the case where a rapid cooling or heating is required depending on the kind of the metal of the strip.